Electric current supply lines for an induction heating coil used with a crucible-free melt zone apparatus

ABSTRACT

An electric current supply line including a pair of parallel conductor elements separated one from another by a hollow dielectric tube, such as composed of quartz or a ceramic and layers of a filler material, for example, silicone rubber, between contiguous metallic surfaces and dielectric surfaces.

United States Patent Keller Oct. 28, 1975 [54] ELECTRIC CURRENT SUPPLY LINES FOR 2,617,002 11/1952 Hasley 174/152 R X AN INDUCTION HEATING COIL USED g 1 l'll 1C a, l'. t WITH A CRUCIBLE'FREE MELT ZONE 2,904,663 9/1959 Emeis et a1 23/273 51 x APPARATUS 3,497,444 2 1970 Paiton 174/15211 x [75] Inventor: Wolfgang Keller, Munich, Germany 315391430 11/1970 Duryee 174/152 R UX 3,688,006 8/1972 Keller 174/152 R X [73] Assignee: Siemens Aktiengesellschaft, Berlin &

' Munich, Germany Primary ExaminerLaramie E. Askin [22] Ffled 1974 Attorney, Agent, or FirmHill, Gross, Simpson, Van [21] Appl. No.: 443,716 Santeen, Steadman, Chiara & Simpson [30] Foreign Application Priority Data Feb. 19, 1973 Germany 2308136 [57] ABSTRACT U-S. 1 An electric urrent upply line including a pair of par- [5 Int- (2]. allel conductor elements eparated one from another F27D 11/06 by a hollow dielectric tube, such as composed of Fleld of Search" 174/15 13H, 16 18, 5055, quartz or a ceramic and layers of a filler material, for 174/50.6, 151, 152 R, 152 GM; 13/1, 26, 27, example, silicone rubber, between contiguous metallic 1; 23/273 SP surfaces and dielectric surfaces.

[56] References cued 1 Claim, 2 Drawing Figures UNITED STATES PATENTS 2,278,974 4/1942 Christensen 174/152 R [z x 7/ 3 l 6 f 1 IZ 1 I I I 8 7 a 1 Silicone 4 I I I I I a Rubber f or 1 Q Polytetrafluoro- 1 ethylene US. Patent Oct. 28, 1975 Whi s I BACKGROUND OF THE INVENTION 1. Field of the Invention i The invention relates to electric current supply lines and a method of producing such lines and, somewhat more particularly, the invention relates to electric current supply lines used with an induction heating coil in producing a molten zone on a semiconductor cyrstalline rod in a cruciblefree zone melt apparatus.

2. Prior Art In a crucible-free zone melting process, a semiconductor crystalline rod is vertically supported within a gas impermeable reaction chamber by suitable support means so that an induction heating coil within the chamber encircles an axial portion of the rod and upon energization of the coil, as by a high frequency current, a molten zone is generated at the encircled portion of the rod. Since the induction heating coil has a relatively small axial dimension in relation to the length of the semiconductor rod, only the portion of the rod which lies in the coil melts. During the course of a cruciblefree zone melting process, relative movement between the rod and the coil is effected. For example, the induction heating coil may be slowly moved in the longitudinal direction of the rod. The process may be carried out in a vacuum or in a protected gas atmosphere.

The induction heating coil is provided with a suitable current via a current supply line which passes through a wall of the reaction chamber and interconnects a source of current with the coil. US. Pat. No. 2,904,663 suggests that such current supply lines be comprised of a pair of conductor tubes of different diameters, which on account of the low inductance are arranged coaxially with one another. In this arrangement, the conductor tube having the largest diameter is passed through a wall of the reaction chamber by means of a gas impermeable seal means so that the tube is displaceable in its longitudinal direction. The space within the inner conductor tube and the space between the outer and inner conductor tubes provide a cyclic flow path for a heatexchange medium. The induction heating coil is supported on the outer conductor tube and is provided with a passage therein which is interconnected to the cyclic flow path within the current supply line so that the heat-exchange medium can circulate throughout the supply line and the coil.

The prior art employed a molded polytetrafluorethylene component for sealing and insulating a current supply line connected with an induction heating coil in a crucible-free zone melt apparatus. These molded components are forced against sealing surfaces by means of a screw which exerts pressure against the molded components. In the event that such an apparatus is subjected to a greater load, such as during the production of large diameter monocrystal rods, the pressure screws must be continuously retightened to insure proper sealing. However, such adjustments are only possible for a limited length of time, for example, until the molded polytetrafluoroethylene components become deformed. Attempts have been made to overcome this drawback by replacing the molded polytetrafluoroethylene components with a silicone rubber which is cast into the sealing and insulating sections and thereafter hardened. However, these attempts have not proven entirely successful since the lengths of the sealing and insulating sections to be filled are too short and thus prevent sufficient mechanical stability. Further, silicone rubber is very soft and under continuous mechanical strain quickly develops cracks or the like.

SUMMARY OF THE INVENTION The invention provides current supply lines comprised vof at least a pair of parallel conductor elements spaced from one another by a dielectric tube composed of a solid insulating material, such as quartz, ceramic or a synthetic material such as polytetrafluoroethylene and layers of a filler compound, such as silicone rubber, joining surfaces of the dielectric tube with contiguous metallic surfaces.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partial schematic illustration in crosssection of a current supply line for interconnecting a source of energy with an induction heating coil, constructed in accordance with the principles of the invention;

and FIG. 2 is a partial front view, with some elements in cross-section, taken substantially along section line lI-II of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENTS The invention provides current supply lines for interconnecting a source of electrical energy with an induction heating coil in a crucible-free melt zone apparatus and a method of producing such lines.

In accordance with the principles of the invention, the main dielectric separating a pair of parallelly arranged conductor elements is comprised of a tube formed of a solid insulating material and the gaps or spaces between contiguous conductor element surfaces and dielectric surfaces (which are relatively small, generally having a maximum dimension of l to 2 mm) are filled with a suitable filler compound, such as silicone rubber so that the resulting supply line has substantially improved electrical properties and better mechanical stability in comparison with the earlier discussed prior art supply lines.

For example, in embodiments of the invention wherein a quartz tube forms the main dielectric element, the resultant current supply line exhibits a tan 8 value of 10 and a dielectric constant e of 3.7. In comparison, substantially identical supply lines having a dielectric formed of only silicone rubber exhibits a tan 8 value of 10' and a dielectric constant e of 3.1. Thus, current supply lines constructed in accordance with the principles of the invention have insulating properties which result in considerably lower losses of the available energy. Further, current supply lines of the invention are not subjected to any substantial field distortions because the dielectric constants of the materials employed are practically identical. Consequently, there is almost no danger of electric sparkovers in a region of the opening into the crucible-free melt zone apparatus.

Referring now to the drawing, a wall 2 of a cruciblefree melt zone apparatus is partially illustrated with the interior of the apparatus facing the left hand side of wall 2. Typically, a crucible-free melt zone apparatus includes a melt zone or reaction chamber 15 wherein a semiconductor crystal rod 16 undergoes treatment. The wall 2 is provided with an opening 2a for communication between the interior and exterior of the apparatus. A current supply line 1 passes through opening Za'and interconnects an induction heating coil 17 with a current supply, such as an HF generator (not shown). The current supply line 1 includes a'hollow metallic ring-like securement means, such as copper tube 3, which is provided with a circular flange 4 for securing the line 1 to the wall 2. The flange 4 is attached to wall 2 by means of screws or bolts 6. A sealing ring 14 is provided between adjacent flange and wall surfaces to insure a gas impermeable connection.

The'current supply line 1 also includes an inner conductor'element, such as copper tube 8 which is separated from outer tube 3 by an insulating means primarily comprised of a solid insulating tube 9, for example, composed of quartz, ceramic or a synthetic material such as polytetrafluoroethylene. The spaces between contiguous surfaces of tube 9 and tubes Sand 8, respectively, are relatively small and are readily filled with a layer of silicone rubber.v The current supply line 1 alsoincludes an outer conductor element, such as a copper tube 11, which is connected, as by soldering,-to an adjacent outer wall of copper tube 3. As shown, the tube 11 passes through an opening in flange 4 so as to be secured to the wall 2. Accordingly, the two metallic conductor elements, tubes 8 and 1 l, are parallelly arranged and spaced fromone another by solid insulating tube 9. The spaces or gaps between contiguous metallic and insulating surfaces are filled with a'layer 10 of asilicone-rubber or a filler compound which includes a base of silicone rubber.

The interior of tube 11 functions asan out-passage and the interior of tube 8 functions as an in-passage for a heat-exchange medium, as schematically indicated by arrows l2 and 13. An induction heating coil 17 has suitable passages therein which are interconnected with tubes 11 and 8 so that a heat-exchange medium can be cyclically flown through the tube and the induction heating coil and prevent thecoil from being excessively heated by current flow and insure that radiati'on heating of the melt zone. occurs.

- .The method embodiment of the invention comprises assembling a current supply line for use with an induction heating coil in a crucible-free zone melt apparatus. The method. includes, fitting a hollow dielectric tube composed of a solid insulating material within an aperture of a securement member, fitting a hollow metallic conductor within'the dielectric tube, fitting a second hollow metallic conductor within a second aperture in the securement member, filling the spaces between contiguous metallic surfaces and insulating material surfaces with afiller compound so that a unitary structure is attained, an d attaching the unitary structure to a wall of a crucible-free zone melt apparatus.

The foregoing is considered as illustrative only of the principles of the invention; Other embodiments of the may be used structural changes'may be made as desired by those skilled in the art without departing from the present-invention and the spirit and scope of-the appended claims. 7

- I claim as my invention: I

l. Foruserin a crucible-free melt zone apparatus having an induction heating coil within a reaction chamber thereof for producing a molten zone on a semiconductor rod mounted within said chamber and including an aperture within the wall of theapparatus for passing a means of supplying current to the induction heating coil, a current supply means comprising:

a hollow metallic ring-like securement member h'aving an axially extending surface and a radially extending surface, said radially extending surface adapted for contacting wall portions adjacent the aperture in said apparatus, said securement member having a first aperture extending along said axial surface of the securement member, said securement member having a second aperture between said axially extending and radially extending surfaces;

a hollow dielectric tube composed of a solid insulating material selected from the group consisting of quartz, ceramic and polytetrafluoroethylene, said dielectric tube having an outer diameter relatively smaller than the diameter of said first aperture in the securement member, said dielectric tube being positioned within said first aperture of the securement member;

a first hollow metallic conductor element having an outer diameter relatively smaller than the inner diameterof said dielectric tube, said first conductor element being positioned within said dielectric tube;

a second hollow metallic conductor element having an outer diameter relatively smaller'than the diarri eter of said second aperture in the securement member, said second conductor element being positioned within saidsecond aperture of the securement member; 7 a layer of a filler compound between contiguous sur faces of said securement member and said dielectric tube;

a layer of a filler compound between contiguous surfaces of said first conductor element and said dielectric tube; and

means on said radially extending flange surface for attaching said radially extending flange surface of the securement member about said aperture in the wall of the cruciblefreezone melt apparatus in a 

1. FOR USE IN A CRUCIBLE-FREE MELT ZONE APPARATUS HAVING AN INTRODUCTION HEATING COIL WITHIN A REACTION CHAMBER THEREOF FOR PRODUCING A MOLTEN ZONE ON A SEMICONDUCTOR ROD MOUNTED WITHIN SAID CHAMBER AND INCLUDING AN APERTURE WITHIN THE WALL OF THE APPARATUS FOR PASSING A MEANS OF SUPPLYING CURRENT TO THE INDUCTION HEATING COIL, A CURRENT MEANS COMPRISING: A HOLLOW METALLIC RING-LIKE SECUREMENT MEMBER HAVING AN AXIALLY EXTENDING SURFACE AND A RADIALLY EXTENDING SURFACE, SAID RADIALLY EXTENDING SURFACE ADAPTED FOR CONTACTING WALL PORTIONS ADJACENT THE APERTURE IN SAID APPARATUS, SAID SECUREMENT MEMBER HAVING A FIRST APERTURE EXTENDING ALONG SAID AXIAL SURFACE OF THE SECUREMENT MEMBER, SAID SECUREMENT MEMBER HAVING A SECOND APERTURE BETWEEN SAID AXIALLY EXTENDING AND RADIALLY EXTENDING SURFACES, A. HOLLOW DIELECTRIC TUBE COMPOUND OF A SOLID INSULATING MATERIAL SELECTED FROM THE GROUP CONSISTING OF QUARTZ, CERAMIC AND POLYTETRAFLUOROETHYLENE, SAID DIELECTRIC TUBE HAVING AN OUTER DIAMETER RELATIVELY SMALLER THAN THE DIAMETER OF SAID FIRST APERTURE IN THE SECUREMENT MEMBER, SAID DIELECTRIC TUBE BEING POSITIONED WITHIN SAID FIRST APERTURE OF THE SECUREMENT MEMBER, A FIRST HOLLOW METALLIC CONDUCTOR ELEMENT HAVING AN OUTER DIAETER RELATIVELY SMALLER THAN THE INNER DIAMETER OF SAID DIELECTRIC TUBE, SAID FIRST CONDUCTOR ELEMENT BEING POSITIONED WITHIN SAID DIELECTRIC TUBE, A SECOND HOLLOW METALLIC CONDUCTOR ELEMENT HAVING AN OUTER DIAMETER RELATIVELY SMALLER THAN THE DIAMETER OF SAID SECOND APERTURE IN THE SECUREMENT MEMBER, SAID SECOND CONDUCTOR ELEMENT BEING POSITIONED WITHIN SAID SECOND APERTURE OF THE SECUREMENT MEMBER, A LAYER OF A FILLER COMPOUND BETWEEN CONTIGUOUS SURFACES OF SAID SECUREMENT MEMBER AND SAID DIELECTRIC TUBE, A LAYER OF A FILLER COMPOUND BETWEEN CONTIGUOUS SURFACES OF SAID FIRST CONDUCTOR ELEMENT AND SAID DIELECTRIC TUBE, AND MEANS ON SAID RADIALLY EXTENDING FLANGE SURFACE FOR ATTACHING SAID RADIALLY EXTENDING FLANGE SURFACE OF THE SECUREMENT MEMBER ABOUT SAID APERTURES IN THE WALL OF THE CRUCIBLEFREE ZONE MELT APPARATUS IN A GAS IMPERMEABLE MANNER. 